U.S. patent number 11,175,378 [Application Number 16/911,141] was granted by the patent office on 2021-11-16 for smart-device-based radar system performing symmetric doppler interference mitigation.
This patent grant is currently assigned to Google LLC. The grantee listed for this patent is Google LLC. Invention is credited to Patrick M. Amihood, Jaime Lien, Cody Blair Wortham.
United States Patent |
11,175,378 |
Amihood , et al. |
November 16, 2021 |
Smart-device-based radar system performing symmetric doppler
interference mitigation
Abstract
Techniques and apparatuses are described that implement a
smart-device-based radar system capable of performing symmetric
Doppler interference mitigation. The radar system employs symmetric
Doppler interference mitigation to filter interference artifacts
caused by the vibration of the radar system or the vibration other
objects. This filtering operation incorporates the interference
artifact within the noise floor, without significantly attenuating
reflections from a desired object. This mitigation can filter each
radar frame independently without a priori knowledge about the
frequency or amplitude of the vibration. The filtering operation is
also independent of the Doppler sampling frequency and can handle
aliasing. By filtering the interference artifacts, the radar system
produces fewer false detections in the presence of vibrations and
can detect objects that would otherwise be masked by the
interference artifact.
Inventors: |
Amihood; Patrick M. (Palo Alto,
CA), Wortham; Cody Blair (San Francisco, CA), Lien;
Jaime (Mountain View, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Google LLC |
Mountain View |
CA |
US |
|
|
Assignee: |
Google LLC (Mountain View,
CA)
|
Family
ID: |
1000005936368 |
Appl.
No.: |
16/911,141 |
Filed: |
June 24, 2020 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20210190902 A1 |
Jun 24, 2021 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/US2019/067490 |
Dec 19, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S
13/89 (20130101); G01S 7/023 (20130101); G01S
13/04 (20130101) |
Current International
Class: |
G01S
7/02 (20060101); G01S 13/04 (20060101); G01S
13/89 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
"International Search Report and Written Opinion", Application No.
PCT/US2019/067490, dated Aug. 18, 2020, 19 pages. cited by
applicant .
Sharma, "A Clutter Based Motion Estimation and Compensation
Technique for a Nonstationary Radar Platform", Apr. 2006, pp.
664-667. cited by applicant .
"Written Opinion", Application No. PCT/US2019/067490, dated May 6,
2021, 9 pages. cited by applicant.
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Primary Examiner: Bythrow; Peter M
Attorney, Agent or Firm: Colby Nipper PLLC
Parent Case Text
PRIORITY APPLICATION
This application claims priority to and is a continuation
application of International Application No. PCT/US2019/067490,
filed Dec. 19, 2019, the disclosure of which is incorporated herein
by reference in its entirety.
Claims
The invention claimed is:
1. A method performed by a radar system embedded within a smart
device, the method comprising: transmitting a radar transmit
signal; receiving a radar receive signal, the radar receive signal
including a portion of the radar transmit signal that is reflected
by at least one object and an interference artifact representing
another portion of the radar transmit signal that is reflected by a
component within the smart device, the interference artifact
representing at least vibration of the component; generating first
information representative of a range-Doppler map based on the
radar receive signal, the interference artifact contributing to
amplitudes of both positive and negative Doppler bins of the
range-Doppler map for at least one range bin; filtering the
interference artifact within the first information to attenuate the
interference artifact and generate second information
representative of a filtered range-Doppler map; and analyzing the
second information to detect the at least one object.
2. The method of claim 1, wherein the amplitudes associated with
the interference artifact are approximately symmetric across the
positive and negative Doppler bins for the at least one range
bin.
3. The method of claim 2, wherein: the amplitudes associated with
the interference artifact are approximately symmetric such that a
first amplitude peak within a first positive Doppler bin of the
positive Doppler bins corresponds to a second amplitude peak within
a first negative Doppler bin of the negative Doppler bins; the
first amplitude peak and the second amplitude peak occur within the
at least one range bin; the first amplitude peak is within twenty
percent of the second amplitude peak; and the first negative
Doppler bin is within at least two Doppler bins of a negative
Doppler bin that corresponds to the first positive Doppler bin.
4. The method of claim 1, wherein: the at least one object
contributes to amplitudes of one or more of the positive Doppler
bins or one or more of the negative Doppler bins for at least one
other range bin; and the filtering of the interference artifact
results in the positive and negative Doppler bins affected by the
interference artifact having a peak amplitude that is smaller than
a peak amplitude of either the one or more positive Doppler bins or
the one or more negative Doppler bins associated with the at least
one object for the at least one other range bin.
5. The method of claim 1, wherein the interference artifact
represents vibration of the radar system during at least a portion
of time that the radar receive signal is received.
6. The method of claim 1, wherein: the interference artifact
further represents at least one of the following: vibration of the
radar system caused by an operation of the component; vibration of
the component; or vibration of another object that is external to
the smart device.
7. The method of claim 1, wherein the filtering of the interference
artifact within the first information comprises: producing third
information representative of a scaled range-Doppler map by:
scaling amplitudes of the positive Doppler bins by amplitudes of
corresponding negative Doppler bins for each range bin of the
range-Doppler map; and scaling amplitudes of the negative Doppler
bins by the amplitudes of the corresponding positive Doppler bins
for each range bin of the range-Doppler map.
8. The method of claim 7, wherein the filtering of the interference
artifact comprises: estimating a noise floor of the first
information representative of the range-Doppler map; and
multiplying the third information representative of the scaled
range-Doppler map by the estimated noise floor to generate the
second information representative of the filtered range-Doppler
map.
9. The method of claim 8, wherein the filtering of the interference
artifact comprises applying a medium filter to the second
information representative of the filtered range-Doppler map, the
medium filter comprising at least one one-dimensional filter or at
least one two-dimensional filter.
10. The method of claim 7, wherein: the filtering of the
interference artifact comprises detecting that at least one other
object contributes to amplitudes of low Doppler bins within the
range-Doppler map, the low Doppler bins including at least a zero
Doppler bin and both a positive Doppler bin and a negative Doppler
bin that are next to the zero Doppler bin; and the scaling the
amplitudes of the positive Doppler bins and the scaling the
amplitudes of the negative Doppler bins comprises, responsive to
detecting the at least one other object, scaling the amplitudes of
Doppler bins that do not include the low Doppler bins.
11. The method of claim 1, wherein: the receiving of the radar
receive signal comprises receiving multiple versions of the radar
receive signal using different antenna elements of the radar
system; and the first information represents multiple range-Doppler
maps respectively associated with the multiple versions of the
radar receive signal.
12. The method of claim 1, wherein the at least one object
comprises a user, the method further comprising: recognizing a
gesture performed by the user by analyzing the second information;
or measuring a vital sign of the user by analyzing the second
information.
13. The method of claim 1, wherein the at least one object
comprises a stylus, the method further comprising recognizing a
gesture performed by a user using the stylus.
14. An apparatus comprising: a component; and a radar system
configured to: transmit a radar transmit signal; receive a radar
receive signal, the radar receive signal including a portion of the
radar transmit signal that is reflected by at least one object and
an interference artifact representing another portion of the radar
transmit signal that is reflected by the component, the
interference artifact representing at least vibration of the
component; generate first information representative of a
range-Doppler map based on the radar receive signal, the
interference artifact contributing to amplitudes of both positive
and negative Doppler bins of the range-Doppler map for at least one
range bin; filter the interference artifact within the first
information to attenuate the interference artifact and generate
second information representative of a filtered range-Doppler map;
and analyze the second information to detect the at least one
object.
15. The apparatus of claim 14, wherein the amplitudes associated
with the interference artifact are approximately symmetric across
the positive and negative Doppler bins for the at least one range
bin.
16. The apparatus of claim 15, wherein: the amplitude associated
with the interference artifact are approximately symmetric such
that a first amplitude peak within a first positive Doppler bin of
the positive Doppler bins corresponds to a second amplitude peak
within a first negative Doppler bin of the negative Doppler bins;
the first amplitude peak and the second amplitude peak occur within
the at least one range bin; the first amplitude peak is within
twenty percent of the second amplitude peak; and the first negative
Doppler bin is within at least two Doppler bins of a negative
Doppler bin that corresponds to the first positive Doppler bin.
17. The apparatus of claim 14, wherein: the at least one object
contributes to amplitudes of one or more of the positive Doppler
bins or one or more of the negative Doppler bins for at least one
other range bin; and the radar system is configured to filter the
interference artifact such that the positive and negative Doppler
bins affected by the interference artifact have a peak amplitude
that is smaller than a peak amplitude of either the one or more
positive Doppler bins or the one or more negative Doppler bins
associated with the at least one object for the at least one other
range bin.
18. The apparatus of claim 14, wherein the interference artifact
represents vibration of the radar system during at least a portion
of time that the radar receive signal is received.
19. The apparatus of claim 14, wherein the interference artifact
further represents at least one of the following: vibration of the
radar system caused by an operation of the component; vibration of
the component; or vibration of another object that is external to
the apparatus.
20. The apparatus of claim 14, wherein the apparatus comprises a
smart device, the smart device comprising one of the following: a
smartphone; a smart watch; a smart speaker; a smart thermostat; a
security camera; a vehicle; or a household appliance.
Description
BACKGROUND
Radars are useful devices that can detect objects. Relative to
other types of sensors, like a camera, a radar can provide improved
performance in the presence of different environmental conditions,
such as low lighting and fog, or with moving or overlapping
objects. Radar can also detect objects through one or more
occlusions, such as a purse or a pocket. While radar has many
advantages, there are many challenges associated with integrating
radar in consumer devices. These challenges include size and layout
constraints of the consumer device, interference generated by other
components within the consumer device, and motion of the consumer
device.
SUMMARY
Techniques and apparatuses are described that implement a
smart-device-based radar system capable of performing symmetric
Doppler interference mitigation. The radar system employs symmetric
Doppler interference mitigation to filter one or more interference
artifacts. An interference artifact can occur due to vibration of
the radar system or vibration of other objects that are observed by
the radar system. Due to the back and forth motion of the
vibration, the interference artifact has both a positive and
negative range rate. As such, the interference artifact contributes
to amplitudes of both positive and negative Doppler bins of a
range-Doppler map generated by the radar system. These amplitudes
are approximately symmetric across the Doppler spectrum for one or
more range bins. If the interference artifact is not filtered, some
radar systems may generate a false detection (or a false alarm)
based on the interference artifact or be unable to detect a desired
object that is obscured by the interference artifact. A false
detection or false alarm represents an erroneous detection that
does not correspond to an object of interest. In general, an
interference artifact refers any type of noise or interference that
presents an approximately symmetric amplitude across the Doppler
spectrum.
Symmetric Doppler interference mitigation exploits the symmetric
amplitude contributions of the interference artifact across the
Doppler spectrum to attenuate the interference artifact. This
filtering operation incorporates the interference artifact within
the noise floor, without significantly attenuating reflections from
the desired object. Symmetric Doppler interference mitigation can
be performed on each radar frame (e.g., each chirp) without a
priori knowledge about the frequency or amplitude of the vibration.
In this way, the radar system can filter interference artifacts
that are generated from a variety of different types of vibrations.
An ability of the symmetric Doppler interference mitigation to
attenuate the interference artifact is also independent of the
Doppler sampling frequency and whether or not aliasing occurs. By
filtering the interference artifacts, the radar system produces
fewer false detections in the presence of vibrations and can detect
objects that would otherwise be masked by the interference
artifact.
Aspects described below include a method performed by a radar
system. The method includes transmitting a radar transmit signal
and receiving a radar receive signal. The radar receive signal
includes an interference artifact and a version of the radar
transmit signal that is reflected by at least one object. The
method additionally includes generating a range-Doppler map based
on the radar receive signal. The interference artifact contributes
to amplitudes of both positive and negative Doppler bins of the
range-Doppler map for at least one range bin. The method further
includes filtering the interference artifact within the
range-Doppler map to attenuate the interference artifact and
generate a filtered range-Doppler map. The method includes
analyzing the filtered range-Doppler map to detect the at least one
object.
Aspects described below also include an apparatus comprising a
radar system configured to perform any of the described
methods.
Aspects described below also include a system with means for
performing symmetric Doppler interference mitigation.
BRIEF DESCRIPTION OF THE DRAWINGS
Apparatuses for and techniques implementing a smart-device-based
radar system capable of performing symmetric Doppler interference
mitigation are described with reference to the following drawings.
The same numbers are used throughout the drawings to reference like
features and components:
FIG. 1 illustrates example environments in which a
smart-device-based radar system capable of performing symmetric
Doppler interference mitigation can be implemented.
FIG. 2-1 illustrates an example implementation of a radar system as
part of a smart device.
FIG. 2-2 illustrates an example location of a radar system relative
to other components within a smartphone.
FIG. 3-1 illustrates operation of an example radar system.
FIG. 3-2 illustrates an example radar framing structure.
FIG. 4 illustrates an example antenna array and an example
transceiver of a radar system.
FIG. 5 illustrates an example scheme implemented by a radar system
for performing symmetric Doppler interference mitigation.
FIG. 6 illustrates an example portion of a hardware-abstraction
module for performing symmetric Doppler interference
mitigation.
FIG. 7 illustrates an example range-Doppler map for performing
symmetric Doppler interference mitigation.
FIG. 8-1 illustrates an example implementation of an interference
mitigation module for performing symmetric Doppler interference
mitigation.
FIG. 8-2 illustrates example regions within a range-Doppler map for
estimating a noise level for symmetric Doppler interference
mitigation.
FIG. 9 illustrates an example method of a radar system for
performing symmetric Doppler interference mitigation.
FIG. 10 illustrates an example computing system embodying, or in
which techniques may be implemented that enable use of, a radar
system capable of performing symmetric Doppler interference
mitigation.
DETAILED DESCRIPTION
Overview
Integrating a radar system within an electronic device can be
challenging. One such challenge involves size or layout constraints
of the electronic device, which may limit where the radar can be
placed relative to other components within the electronic device.
In some cases, an operation of the component causes the radar
system to vibrate (e.g., move back and forth across one or more
dimensions). A speaker, for instance, can generate an audible sound
that causes the radar to vibrate with a frequency that is dependent
on the frequency of the audible sound and with an amplitude that is
dependent on a volume of the speaker. Additionally or
alternatively, the electronic device, which houses the radar
system, may vibrate due to external forces. These vibrations can
occur as a user walks with the electronic device or rides in a
vehicle (e.g., a car, a bus, a train, or a plane).
Due to the vibrations, the radar system observes one or more
interference artifacts within a received radar signal. To the radar
system, the interference artifact can appear to be one or more
moving objects. It can be challenging for the radar system to
distinguish between an object of interest (e.g., a desired object)
within the external environment and the interference artifact. As
such, the radar system may generate one or more false detections
based on the interference artifact, which increases the radar
system's false-alarm rate and degrades the performance of the radar
system. Sometimes the interference artifact can mask the desired
object and prevent the radar system from detecting the object.
In other cases, the radar system observes objects that are
vibrating. These objects can be internal or external to the
electronic device. Sometimes multipath causes the radar system to
observe an interference artifact associated with the vibrating
object at a range that is farther than the range to the vibrating
object. The interference artifact associated with the vibrating
object can similarly result in a false detection and mask other
desired objects.
Some techniques may try to reduce the occurrence of interference
artifacts by isolating the radar system from internal components
within the electronic device that cause the radar system to
vibrate. However, this may increase cost of the electronic device
and increase a footprint of the radar system. In some cases, this
may result in the radar system being placed in a sub-optimal
location that makes it challenging for the radar system to perform
its intended function, such as detecting the user. In other cases,
it may not be possible to isolate the radar system from the
internal component due to size or layout constraints of the
electronic device.
Other techniques may limit a field of view of the radar system to
reduce a likelihood of the radar system observing components within
the electronic device that vibrate. However, this technique also
limits the volume of space in which the radar system can detect a
desired object. As such, effective operation of the radar system is
limited.
In contrast, this document describes techniques and devices that
implement a smart-device-based radar system capable of performing
symmetric Doppler interference mitigation. The radar system employs
symmetric Doppler interference mitigation to filter one or more
interference artifacts. An interference artifact can occur due to
vibration of the radar system or vibration of other objects that
are observed by the radar system. Due to the back and forth motion
of the vibration, the interference artifact has both a positive and
negative range rate. As such, the interference artifact contributes
to amplitudes of both positive and negative Doppler bins of a
range-Doppler map generated by the radar system. These amplitudes
are approximately symmetric across the Doppler spectrum for one or
more range bins. If the interference artifact is not filtered, some
radar systems may generate a false detection (or a false alarm)
based on the interference artifact or be unable to detect a desired
object that is obscured by the interference artifact. A false
detection or false alarm represents an erroneous detection that
does not correspond to an object of interest. In general, an
interference artifact refers any type of noise or interference that
presents an approximately symmetric amplitude across the Doppler
spectrum.
Symmetric Doppler interference mitigation exploits the symmetric
amplitude contributions of the interference artifact across the
Doppler spectrum to attenuate the interference artifact. This
filtering operation incorporates the interference artifact within
the noise floor, without significantly attenuating reflections from
the desired object. Symmetric Doppler interference mitigation can
be performed on each radar frame (e.g., each chirp) without a
priori knowledge about the frequency or amplitude of the vibration.
In this way, the radar system can filter interference artifacts
that are generated from a variety of different types of vibrations.
An ability of the symmetric Doppler interference mitigation to
attenuate the interference artifact is also independent of the
Doppler sampling frequency and whether or not aliasing occurs. By
filtering the interference artifacts, the radar system produces
fewer false detections in the presence of vibrations and can detect
objects that would otherwise be masked by the interference
artifact.
EXAMPLE ENVIRONMENT
FIG. 1 is an illustration of example environments 100-1 to 100-4 in
which techniques using, and an apparatus including, a
smart-device-based radar system capable of performing symmetric
Doppler interference mitigation may be embodied. In the depicted
environments 100-1 to 100-4, a smart device 104 includes a radar
system 102 capable of detecting one or more objects (e.g., users)
in the presence of one or more interference artifacts. As described
above, an interference artifact has an approximately symmetric
Doppler response. The smart device 104 is shown to be a smartphone
in environments 100-1 to 100-4.
In the environments 100-1 to 100-4, the radar system 102 observes
one or more interference artifacts. These interference artifacts
can appear due to an operation of a component within the smart
device 104 causing the radar system 102 to vibrate, external forces
causing the radar system 102 to vibrate, or the radar system 102
observing another vibrating object that is internal or external to
the smart device 104. Generally, a vibration refers to a back and
forth motion across one or more dimensions. This motion can repeat
over time with an amplitude that decays or remains relatively
steady.
In the environment 100-1, the smart device 104 produces an audible
sound. The audible sound can be a single tone, a ring tone, an
alarm bell, or music, for instance. While the audible sound is
produced, a user makes a reach gesture, which decreases a distance
between the smart device 104 and the user's hand. Although the
audible sound causes the radar system 102 to vibrate, the radar
system 102 uses symmetric Doppler interference mitigation to filter
the interference artifact generated by the audible sound. By
filtering the interference artifact, the radar system 102 can
detect the reach gesture. Responsive to detecting the reach
gesture, the smart device 104 can dynamically adjust a volume of
the audible sound based on the distance between the user's hand and
the radar system 102.
In some implementations, the radar system can analyze the
interference artifact prior to filtering the interference artifact.
For example, the radar system 102 can analyze the interference
artifact to recognize the type of audible sound produced. This can
include identifying the genre of music, recognizing a particular
artist, or identifying a title of a song. The radar system 102 can
provide information to the smart device 104, which can display the
information to the user. In this manner, the radar system 102 can
analyze the frequency and amplitude of its vibrations to perform
music recognition.
In environment 100-2, the user makes a swipe gesture by moving a
hand above the smart device 104 along a horizontal dimension (e.g.,
from a left side of the smart device 104 to a right side of the
smart device 104). While the gesture is performed, the table
vibrates due to the user placing their mug on the table. Although
this causes the smart device 104, and therefore the radar system
102, to vibrate, the radar system 102 uses symmetric Doppler
interference mitigation to filter the resulting interference
artifact and detect the swipe gesture. Responsive to detecting the
swipe gesture, the smart device 104 displays new content to the
user. In environments 100-1 and 100-2, the user performs a gesture
using an appendage or body part. Alternatively, the user can
perform a gesture using a stylus, a hand-held object, a ring, or
any type of material that can reflect radar signals.
The radar system 102 can also recognize other types of gestures or
motions not shown in FIG. 1. Example types of gestures include a
knob-turning gesture in which a user curls their fingers to grip an
imaginary doorknob and rotate their fingers and hand in a clockwise
or counter-clockwise fashion to mimic an action of turning the
imaginary doorknob. Another example type of gesture includes a
spindle-twisting gesture, which a user performs by rubbing a thumb
and at least one other finger together.
The gestures can be two-dimensional, such as those used with
touch-sensitive displays (e.g., a two-finger pinch, a two-finger
spread, or a tap). The gestures can also be three-dimensional, such
as many sign-language gestures, e.g., those of American Sign
Language (ASL) and other sign languages worldwide. Upon detecting
each of these gestures, the smart device 104 can perform an action,
such as display new content, move a cursor, activate one or more
sensors, open an application, and so forth. In this way, the radar
system 102 provides touch-free control of the smart device 104.
In environment 100-3, the user walks with the smart device 104.
Although the smart device 104 vibrates with each step the user
takes, the radar system 102 uses symmetric Doppler interference
mitigation to filter the resulting interference artifact. In this
way, the radar system 102 avoids producing false detections based
on the interference artifact. Additionally, if a haptic sensor
within the smart device 104 activates, the symmetric Doppler
interference mitigation can also filter an interference artifact
resulting from the haptic sensor to further avoid additional false
detections.
In environment 100-4, the user interacts with the smart device 104
while in a moving vehicle. Although rough roads may cause the
vehicle to vibrate, the radar system 102 uses symmetric Doppler
interference mitigation to filter an interference artifact
resulting from vibration of the walls of the vehicle or vibration
of the radar system 102 itself. If the smart device 104 includes a
piezoelectric touch screen, the radar system 102 can also use
symmetric Doppler interference mitigation to filter an interference
artifact resulting from the user interacting with the touch
screen.
The radar system 102 can perform other types of operations besides
gesture recognition or object detection. For example, the radar
system 102 can determine one or more characteristics of an object
(e.g., location, movement, or composition), generate a
three-dimensional map of a surrounding environment for contextual
awareness, detect and track multiple users to enable both users to
interact with the smart device 104, and perform human vital-sign
detection.
Some implementations of the radar system 102 are particularly
advantageous as applied in the context of smart devices 104, for
which there is a convergence of issues. This can include a need for
limitations in a spacing and layout of the radar system 102 and low
power. Exemplary overall lateral dimensions of the smart device 104
can be, for example, approximately eight centimeters by
approximately fifteen centimeters. Exemplary footprints of the
radar system 102 can be even more limited, such as approximately
four millimeters by six millimeters with antennas included.
Exemplary power consumption of the radar system 102 may be on the
order of a few milliwatts to tens of milliwatts (e.g., between
approximately two milliwatts and twenty milliwatts). The
requirement of such a limited footprint and power consumption for
the radar system 102 enables the smart device 104 to include other
desirable features in a space-limited package (e.g., a camera
sensor, a fingerprint sensor, a display, and so forth). The smart
device 104 and the radar system 102 are further described with
respect to FIG. 2.
FIG. 2-1 illustrates the radar system 102 as part of the smart
device 104. The smart device 104 is illustrated with various
non-limiting example devices including a desktop computer 104-1, a
tablet 104-2, a laptop 104-3, a television 104-4, a computing watch
104-5, computing glasses 104-6, a gaming system 104-7, a microwave
104-8, and a vehicle 104-9. Other devices may also be used, such as
a home service device, a smart speaker, a smart thermostat, a
security camera, a baby monitor, a Wi-Fi.TM. router, a drone, a
trackpad, a drawing pad, a netbook, an e-reader, a home-automation
and control system, a wall display, and another home appliance.
Note that the smart device 104 can be wearable, non-wearable but
mobile, or relatively immobile (e.g., desktops and appliances). The
radar system 102 can be used as a stand-alone radar system or used
with, or embedded within, many different smart devices 104 or
peripherals, such as in control panels that control home appliances
and systems, in automobiles to control internal functions (e.g.,
volume, cruise control, or even driving of the car), or as an
attachment to a laptop computer to control computing applications
on the laptop.
The smart device 104 includes one or more computer processors 202
and computer-readable media 204, which includes memory media and
storage media. Applications and/or an operating system (not shown)
embodied as computer-readable instructions on the computer-readable
media 204 can be executed by the computer processor 202 to provide
some of the functionalities described herein. The computer-readable
media 204 also includes a radar-based application 206, which uses
radar data generated by the radar system 102 to perform a function,
such as presence detection, gesture-based touch-free control,
collision avoidance for autonomous driving, human vital-sign
notification, and so forth.
The smart device 104 can also include a network interface 208 for
communicating data over wired, wireless, or optical networks. For
example, the network interface 208 may communicate data over a
local-area-network (LAN), a wireless local-area-network (WLAN), a
personal-area-network (PAN), a wire-area-network (WAN), an
intranet, the Internet, a peer-to-peer network, point-to-point
network, a mesh network, and the like. The smart device 104 may
also include a display (not shown).
The radar system 102 includes a communication interface 210 to
transmit the radar data to a remote device, though this need not be
used when the radar system 102 is integrated within the smart
device 104. In general, the radar data provided by the
communication interface 210 is in a format usable by the
radar-based application 206.
The radar system 102 also includes at least one antenna array 212
and at least one transceiver 214 to transmit and receive radar
signals. The antenna array 212 includes at least one transmit
antenna element and at least one receive antenna element. In some
situations, the antenna array 212 includes multiple transmit
antenna elements to implement a multiple-input multiple-output
(MIMO) radar capable of transmitting multiple distinct waveforms at
a given time (e.g., a different waveform per transmit antenna
element). The antenna elements can be circularly polarized,
horizontally polarized, vertically polarized, or a combination
thereof.
In some implementations, the antenna array 212 includes two or more
receive antenna elements for digital beamforming. The receive
antenna elements of the antenna array 212 can be positioned in a
one-dimensional shape (e.g., a line) or a two-dimensional shape
(e.g., a rectangular arrangement, a triangular arrangement, or an
"L" shape arrangement) for implementations that include three or
more receive antenna elements. The one-dimensional shape enables
the radar system 102 to measure one angular dimension (e.g., an
azimuth or an elevation) while the two-dimensional shape enables
the radar system 102 to measure two angular dimensions (e.g., to
determine both an azimuth angle and an elevation angle of the
object 302). An element spacing associated with the receive antenna
elements can be less than, greater than, or equal to half a center
wavelength of the radar signal.
Using the antenna array 212, the radar system 102 can form beams
that are steered or un-steered, wide or narrow, or shaped (e.g.,
hemisphere, cube, fan, cone, cylinder). The steering and shaping
can be achieved through analog beamforming or digital beamforming.
The one or more transmitting antenna elements can have, for
instance, an un-steered omnidirectional radiation pattern or can
produce a wide steerable beam to illuminate a large volume of
space. To achieve target angular accuracies and angular
resolutions, the receiving antenna elements can be used to generate
hundreds or thousands of narrow steered beams with digital
beamforming. In this way, the radar system 102 can efficiently
monitor an external environment and detect one or more users.
The transceiver 214 includes circuitry and logic for transmitting
and receiving radar signals via the antenna array 212. Components
of the transceiver 214 can include amplifiers, mixers, switches,
analog-to-digital converters, or filters for conditioning the radar
signals. The transceiver 214 also includes logic to perform
in-phase/quadrature (I/Q) operations, such as modulation or
demodulation. A variety of modulations can be used, including
linear frequency modulations, triangular frequency modulations,
stepped frequency modulations, or phase modulations. Alternatively,
the transceiver 214 can produce radar signals having a relatively
constant frequency or a single tone. The transceiver 214 can be
configured to support continuous-wave or pulsed radar
operations.
A frequency spectrum (e.g., range of frequencies) that the
transceiver 214 uses to generate the radar signals can encompass
frequencies between 1 and 400 gigahertz (GHz), between 4 and 100
GHz, between 1 and 24 GHz, between 2 and 4 GHz, between 57 and 64
GHz, or at approximately 2.4 GHz. In some cases, the frequency
spectrum can be divided into multiple sub-spectrums that have
similar or different bandwidths. The bandwidths can be on the order
of 500 megahertz (MHz), 1 GHz, 2 GHz, and so forth. Different
frequency sub-spectrums may include, for example, frequencies
between approximately 57 and 59 GHz, 59 and 61 GHz, or 61 and 63
GHz. Although the example frequency sub-spectrums described above
are contiguous, other frequency sub-spectrums may not be
contiguous. To achieve coherence, multiple frequency sub-spectrums
(contiguous or not) that have a same bandwidth may be used by the
transceiver 214 to generate multiple radar signals, which are
transmitted simultaneously or separated in time. In some
situations, multiple contiguous frequency sub-spectrums may be used
to transmit a single radar signal, thereby enabling the radar
signal to have a wide bandwidth.
The radar system 102 also includes one or more system processors
216 and a system media 218 (e.g., one or more computer-readable
storage media). The system media 218 optionally includes a
hardware-abstraction module 220. The system media 218 also includes
an interference mitigation module 222. The hardware-abstraction
module 220 and the interference mitigation module 222 can be
implemented using hardware, software, firmware, or a combination
thereof. In this example, the system processor 216 implements the
hardware-abstraction module 220 and the interference mitigation
module 222. Together, the hardware-abstraction module 220 and the
interference mitigation module 222 enable the system processor 216
to process responses from the receive antenna elements in the
antenna array 212 to detect a user, determine a position of the
object, and/or recognize a gesture performed by the user.
In an alternative implementation (not shown), the
hardware-abstraction module 220 and the interference mitigation
module 222 are included within the computer-readable media 204 and
implemented by the computer processor 202. This enables the radar
system 102 to provide the smart device 104 raw data via the
communication interface 210 such that the computer processor 202
can process the raw data for the radar-based application 206.
The hardware-abstraction module 220 transforms raw data provided by
the transceiver 214 into hardware-agnostic radar data, which can be
processed by the interference mitigation module 222. In particular,
the hardware-abstraction module 220 conforms complex radar data
from a variety of different types of radar signals to an expected
input of the interference mitigation module 222. This enables the
interference mitigation module 222 to process different types of
radar signals received by the radar system 102, including those
that utilize different modulations schemes for frequency-modulated
continuous-wave radar, phase-modulated spread spectrum radar, or
impulse radar. The hardware-abstraction module 220 can also
normalize complex radar data from radar signals with different
center frequencies, bandwidths, transmit power levels, or
pulsewidths.
Additionally, the hardware-abstraction module 220 conforms complex
radar data generated using different hardware architectures.
Different hardware architectures can include different antenna
arrays 212 positioned on different surfaces of the smart device 104
or different sets of antenna elements within an antenna array 212.
By using the hardware-abstraction module 220, the interference
mitigation module 222 can process complex radar data generated by
different sets of antenna elements with different gains, different
sets of antenna elements of various quantities, or different sets
of antenna elements with different antenna element spacings.
By using the hardware-abstraction module 220, the interference
mitigation module 222 can operate in radar systems 102 with
different limitations that affect the available radar modulation
schemes, transmission parameters, or types of hardware
architectures. The hardware-abstraction module 220 is further
described with respect to FIG. 6.
The interference mitigation module 222 filters the
hardware-agnostic radar data to attenuate one or more interference
artifacts resulting from vibration of the radar system 102 or
vibration of other objects detected by the radar system 102. Due to
the back and forth motion of the vibration, the interference
artifact has both a positive and negative range rate. As such, the
interference artifact contributes to amplitudes across both
positive and negative Doppler bins of a range-Doppler map generated
by the radar system. In contrast, most desired objects contribute
to amplitudes across either positive or negative Doppler bins. In
other words, the amplitudes resulting from the interference
artifact are approximately symmetric across the Doppler bins,
whereas the amplitudes resulting from the desired object are
one-sided and not symmetrical. The interference mitigation module
222 exploits this difference to attenuate the interference artifact
without significantly attenuating the desired object. In some
cases, the interference mitigation module 222 can also analyze and
adjust phase information within the range-Doppler map to mitigate
the effects of the interference artifact. The interference
mitigation module 222 is further described with respect to FIG.
8-1.
The interference mitigation module 222 produces filtered radar
data, which can be further analyzed by the system processor 216.
For example, the system processor 216 can process the filtered
radar data to generate radar-application data for the radar-based
application 206. Example types of radar-application data include a
position of a user, movement of the user, a type of gesture
performed by the user, a measured vital-sign of the user, a
collision alert, or characteristics of an object.
FIG. 2-2 illustrates an example location of the radar system 102
relative to other components within the smart device 104. In this
example, the smart device 104 is shown to be a smartphone 104-10.
An exterior of the smartphone 104-10 includes an exterior housing
224 and an exterior viewing panel 226. As an example, the exterior
housing 224 has a vertical height of approximately 147 millimeters
(mm), a horizontal length of approximately 69 mm, and a width of
approximately 8 mm. The exterior housing 224 can be composed of
metal material, for instance.
The exterior viewing panel 226 forms an exterior face of the
smartphone 104-10 and has a vertical height of approximately 139 mm
and a horizontal length of approximately 61 mm. The exterior
viewing panel 226 includes cut-outs for various components that are
positioned within an interior of the smartphone 104-10 (e.g.,
positioned beneath the exterior viewing panel 226). These
components are further described below.
The exterior viewing panel 226 can be formed using various types of
glass or plastics that are found within display screens. In some
implementations, the exterior viewing panel 226 has a dielectric
constant (e.g., a relative permittivity) between approximately four
and ten, which attenuates or distorts radar signals. As such, the
exterior viewing panel 226 is opaque or semi-transparent to a radar
signal and can cause a portion of a transmitted or received radar
signal to be reflected.
At least a portion of the radar system 102, such as an integrated
circuit that includes the antenna array 212 and the transceiver
214, is positioned beneath the exterior viewing panel 226 and near
an edge of the smartphone 104-10. As an example, the integrated
circuit has a vertical height of approximately 5 mm, a horizontal
length of approximately 6.5 mm, and a thickness of approximately
0.85 mm (within +/-0.1 mm along each dimension). These dimensions
enable the integrated circuit to fit between the exterior housing
224 and a display element 228. The vertical height of the
integrated circuit can be similar to other components that are
positioned near the edge of the smartphone 104-10 so as to avoid
reducing a size of the display element 228.
In this example implementation, the antenna array 212 is oriented
towards (e.g., faces) the exterior viewing panel 226. As such, the
integrated circuit radiates through the exterior viewing panel 226
(e.g., transmits and receives the radar signals that propagate
through the exterior viewing panel 226). If the exterior viewing
panel 226 behaves as an attenuator, the radar system 102 can adjust
a frequency or a steering angle of a transmitted radar signal to
mitigate the effects of the attenuator instead of increasing
transmit power. As such, the radar system 102 can realize enhanced
accuracy and longer ranges for detecting the user without
increasing power consumption.
The display element 228 displays images that are viewed through the
exterior viewing panel 226. As shown, the antenna array 212 of the
radar system 102 is oriented towards (e.g., faces) a same direction
as the display element 228 such that the radar integrated circuit
238 transmits radar signals towards a user that is looking at the
display element 228.
In this example, the integrated circuit transmits and receives
radar signals with frequencies between approximately 57 and 64 GHz.
This mitigates electromagnetic interference with a wireless
communication system of the smartphone 104-10, which uses
frequencies below 20 GHz, for instance. Transmitting and receiving
radar signals with millimeter wavelengths further enables the
integrated circuit to realize the above footprint.
A depicted interior of the smartphone 104-10 includes the
integrated circuit of the radar system 102, the display element
228, an infrared sensor 230, a speaker 232, a proximity sensor 234,
an ambient light sensor 236, a camera 238, and another infrared
sensor 240. The integrated circuit of the radar system 102, the
infrared sensor 230, the speaker 232, the proximity sensor 234, the
ambient light sensor 236, the camera 238, and the infrared sensor
240 are positioned beneath an upper portion of the exterior viewing
panel 226. The display element 228 is positioned beneath the lower
portion of the exterior viewing panel 226. In this example, a
distance between a top edge of the display element 228 and a top
edge of the exterior viewing panel 226 (D.sub.GD) is approximately
6.2 mm.
The infrared sensors 230 and 240 can be used for facial
recognition. To conserve power, the infrared sensors 230 and 240
operate in an off-state when not in use. However, a warm-up
sequence associated with transitioning the infrared sensors 230 and
240 from the off-state to an on-state can require a significant
amount of time, such as a half-second or more. This can cause a
delay in execution of the facial recognition. To reduce this time
delay, the radar system 102 proactively detects the user reaching
towards or approaching the smartphone 104-10 and initiates the
warm-up sequence prior to the user touching the smartphone 104-10.
As such, the infrared sensors 230 and 240 can be in the on-state
sooner and reduce a time the user waits for the facial recognition
to complete.
In this example, the integrated circuit of the radar system 102 is
positioned between the infrared sensor 230 and the speaker 232. A
distance between the integrated circuit and the speaker 232
(D.sub.SR) is approximately 0.93 mm or less. As such, the radar
system 102 is within close proximity to the speaker 232 and can
vibrate while the speaker 232 produces audible sounds. By using
symmetric Doppler interference mitigation, the radar system 102 can
operate while the speaker 232 is producing the audible sounds
without increasing the false-alarm rate.
FIG. 3-1 illustrates an example operation of the radar system 102.
In the depicted configuration, the radar system 102 is implemented
as a frequency-modulated continuous-wave radar. However, other
types of radar architectures can be implemented, as described above
with respect to FIG. 2-1. In environment 300, a user 302 is located
at a particular slant range 304 from the radar system 102. To
detect the user 302, the radar system 102 transmits a radar
transmit signal 306. At least a portion of the radar transmit
signal 306 is reflected by the user 302. This reflected portion
represents a radar receive signal 308. The radar system 102
receives the radar receive signal 308 and processes the radar
receive signal 308 to extract data for the radar-based application
206. As depicted, an amplitude of the radar receive signal 308 is
smaller than an amplitude of the radar transmit signal 306 due to
losses incurred during propagation and reflection.
The radar transmit signal 306 includes a sequence of chirps 310-1
to 310-N, where N represents a positive integer greater than one.
The radar system 102 can transmit the chirps 310-1 to 310-N in a
continuous burst or transmit the chirps 310-1 to 310-N as
time-separated pulses, as further described with respect to FIG.
3-2. A duration of each chirp 310-1 to 310-N can be on the order of
tens or thousands of microseconds (e.g., between approximately 30
microseconds (.mu.s) and 5 milliseconds (ms)), for instance.
Individual frequencies of the chirps 310-1 to 310-N can increase or
decrease over time. In the depicted example, the radar system 102
employs a two-slope cycle (e.g., triangular frequency modulation)
to linearly increase and linearly decrease the frequencies of the
chirps 310-1 to 310-N over time. The two-slope cycle enables the
radar system 102 to measure the Doppler frequency shift caused by
motion of the user 302. In general, transmission characteristics of
the chirps 310-1 to 310-N (e.g., bandwidth, center frequency,
duration, and transmit power) can be tailored to achieve a
particular detection range, range resolution, or doppler
sensitivity for detecting one or more characteristics the user 302
or one or more actions performed by the user 302.
At the radar system 102, the radar receive signal 308 represents a
delayed version of the radar transmit signal 306. The amount of
delay is proportional to the slant range 304 (e.g., distance) from
the antenna array 212 of the radar system 102 to the user 302. In
particular, this delay represents a summation of a time it takes
for the radar transmit signal 306 to propagate from the radar
system 102 to the user 302 and a time it takes for the radar
receive signal 308 to propagate from the user 302 to the radar
system 102. If the user 302 and/or the radar system 102 is moving,
the radar receive signal 308 is shifted in frequency relative to
the radar transmit signal 306 due to the Doppler effect. In other
words, characteristics of the radar receive signal 308 are
dependent upon motion of the hand and/or motion of the radar system
102. Similar to the radar transmit signal 306, the radar receive
signal 308 is composed of one or more of the chirps 310-1 to
310-N.
The multiple chirps 310-1 to 310-N enable the radar system 102 to
make multiple observations of the user 302 over a predetermined
time period. A radar framing structure determines a timing of the
chirps 310-1 to 310-N, as further described with respect to FIG.
3-2.
FIG. 3-2 illustrates an example radar framing structure 312 for
symmetric Doppler interference mitigation. In the depicted
configuration, the radar framing structure 312 includes three
different types of frames. At a top level, the radar framing
structure 312 includes a sequence of main frames 314, which can be
in the active state or the inactive state. Generally speaking, the
active state consumes a larger amount of power relative to the
inactive state. At an intermediate level, the radar framing
structure 312 includes a sequence of feature frames 316, which can
similarly be in the active state or the inactive state. Different
types of feature frames 316 include a pulse-mode feature frame 318
(shown at the bottom-left of FIG. 3-2) and a burst-mode feature
frame 320 (shown at the bottom-right of FIG. 3-2). At a low level,
the radar framing structure 312 includes a sequence of radar frames
(RF) 322, which can also be in the active state or the inactive
state.
The radar system 102 transmits and receives a radar signal during
an active radar frame 322. In some situations, the radar frames 322
are individually analyzed for basic radar operations, such as
search and track, clutter map generation, user location
determination, and so forth. Radar data collected during each
active radar frame 322 can be saved to a buffer after completion of
the radar frame 322 or provided directly to the system processor
216 of FIG. 2.
The radar system 102 analyzes the radar data across multiple radar
frames 322 (e.g., across a group of radar frames 322 associated
with an active feature frame 316) to identify a particular feature.
Example types of features include a particular type of motion, a
motion associated with a particular appendage (e.g., a hand or
individual fingers), and a feature associated with different
portions of the gesture. To recognize a gesture performed by the
user 302 during an active main frame 314, the radar system 102
analyzes the radar data associated with one or more active feature
frames 316.
A duration of the main frame 314 may be on the order of
milliseconds or seconds (e.g., between approximately 10 ms and 10
seconds (s)). After active main frames 314-1 and 314-2 occur, the
radar system 102 is inactive, as shown by inactive main frames
314-3 and 314-4. A duration of the inactive main frames 314-3 and
314-4 is characterized by a deep sleep time 324, which may be on
the order of tens of milliseconds or more (e.g., greater than 50
ms). In an example implementation, the radar system 102 turns off
all of the active components (e.g., an amplifier, an active filter,
a voltage-controlled oscillator (VCO), a voltage-controlled buffer,
a multiplexer, an analog-to-digital converter, a phase-lock loop
(PLL) or a crystal oscillator) within the transceiver 214 to
conserve power during the deep sleep time 324.
In the depicted radar framing structure 312, each main frame 314
includes K feature frames 316, where K is a positive integer. If
the main frame 314 is in the inactive state, all of the feature
frames 316 associated with that main frame 314 are also in the
inactive state. In contrast, an active main frame 314 includes J
active feature frames 316 and K-J inactive feature frames 316,
where J is a positive integer that is less than or equal to K. A
quantity of feature frames 316 can be adjusted based on a
complexity of the environment or a complexity of a gesture. For
example, a main frame 314 can include a few to a hundred feature
frames 316 (e.g., K may equal 2, 10, 30, 60, or 100). A duration of
each feature frame 316 may be on the order of milliseconds (e.g.,
between approximately 1 ms and 50 ms).
To conserve power, the active feature frames 316-1 to 316-J occur
prior to the inactive feature frames 316-(J+1) to 316-K. A duration
of the inactive feature frames 316-(J+1) to 316-K is characterized
by a sleep time 326. In this way, the inactive feature frames
316-(J+1) to 316-K are consecutively executed such that the radar
system 102 can be in a powered-down state for a longer duration
relative to other techniques that may interleave the inactive
feature frames 316-(J+1) to 316-K with the active feature frames
316-1 to 316-J. Generally speaking, increasing a duration of the
sleep time 326 enables the radar system 102 to turn off components
within the transceiver 214 that require longer start-up times.
Each feature frame 316 includes L radar frames 322, where L is a
positive integer that may or may not be equal to J or K. In some
implementations, a quantity of radar frames 322 may vary across
different feature frames 316 and may comprise a few frames or
hundreds of frames (e.g., L may equal 5, 15, 30, 100, or 500). A
duration of a radar frame 322 may be on the order of tens or
thousands of microseconds (e.g., between approximately 30 .mu.s and
5 ms). The radar frames 322 within a particular feature frame 316
can be customized for a predetermined detection range, range
resolution, or doppler sensitivity, which facilitates detection of
a particular feature or gesture. For example, the radar frames 322
may utilize a particular type of modulation, bandwidth, frequency,
transmit power, or timing. If the feature frame 316 is in the
inactive state, all of the radar frames 322 associated with that
feature frame 316 are also in the inactive state.
The pulse-mode feature frame 318 and the burst-mode feature frame
320 include different sequences of radar frames 322. Generally
speaking, the radar frames 322 within an active pulse-mode feature
frame 318 transmit pulses that are separated in time by a
predetermined amount. This disperses observations over time, which
can make it easier for the radar system 102 to recognize a gesture
due to larger changes in the observed chirps 310-1 to 310-N within
the pulse-mode feature frame 318 relative to the burst-mode feature
frame 320. In contrast, the radar frames 322 within an active
burst-mode feature frame 320 transmit pulses continuously across a
portion of the burst-mode feature frame 320 (e.g., the pulses are
not separated by a predetermined amount of time). This enables an
active-burst-mode feature frame 320 to consume less power than the
pulse-mode feature frame 318 by turning off a larger quantity of
components, including those with longer start-up times, as further
described below.
Within each active pulse-mode feature frame 318, the sequence of
radar frames 322 alternates between the active state and the
inactive state. Each active radar frame 322 transmits a chirp 310
(e.g., a pulse), which is illustrated by a triangle. A duration of
the chirp 310 is characterized by an active time 328. During the
active time 328, components within the transceiver 214 are
powered-on. During a short-idle time 330, which includes the
remaining time within the active radar frame 322 and a duration of
the following inactive radar frame 322, the radar system 102
conserves power by turning off one or more active components within
the transceiver 214 that have a start-up time within a duration of
the short-idle time 330.
An active burst-mode feature frame 320 includes P active radar
frames 322 and L-P inactive radar frames 322, where P is a positive
integer that is less than or equal to L. To conserve power, the
active radar frames 322-1 to 322-P occur prior to the inactive
radar frames 322-(P+1) to 322-L. A duration of the inactive radar
frames 322-(P+1) to 322-L is characterized by a long-idle time 332.
By grouping the inactive radar frames 322-(P+1) to 322-L together,
the radar system 102 can be in a powered-down state for a longer
duration relative to the short-idle time 330 that occurs during the
pulse-mode feature frame 318. Additionally, the radar system 102
can turn off additional components within the transceiver 214 that
have start-up times that are longer than the short-idle time 330
and shorter than the long-idle time 332.
Each active radar frame 322 within an active burst-mode feature
frame 320 transmits a portion of the chirp 310. In this example,
the active radar frames 322-1 to 322-P alternate between
transmitting a portion of the chirp 310 that increases in frequency
and a portion of the chirp 310 that decreases in frequency.
The radar framing structure 312 enables power to be conserved
through adjustable duty cycles within each frame type. A first duty
cycle 334 is based on a quantity of active feature frames 316 (J)
relative to a total quantity of feature frames 316 (K). A second
duty cycle 336 is based on a quantity of active radar frames 322
(e.g., L/2 or P) relative to a total quantity of radar frames 322
(L). A third duty cycle 338 is based on a duration of the chirp 310
relative to a duration of a radar frame 322.
Consider an example radar framing structure 312 for a power state
that consumes approximately 2 milliwatts (mW) of power and has a
main-frame update rate between approximately 1 and 4 hertz (Hz). In
this example, the radar framing structure 312 includes a main frame
314 with a duration between approximately 250 ms and 1 second. The
main frame 314 includes thirty-one pulse-mode feature frames 318
(e.g., K is equal to 31). One of the thirty-one pulse-mode feature
frames 318 is in the active state. This results in the duty cycle
334 being approximately equal to 3.2%. A duration of each
pulse-mode feature frame 318 is between approximately 8 and 32 ms.
Each pulse-mode feature frame 318 is composed of eight radar frames
322 (e.g., L is equal to 8). Within the active pulse-mode feature
frame 318, all eight radar frames 322 are in the active state. This
results in the duty cycle 336 being equal to 100%. A duration of
each radar frame 322 is between approximately 1 and 4 ms. An active
time 328 within each of the active radar frames 322 is between
approximately 32 and 128 .mu.s. As such, the resulting duty cycle
338 is approximately 3.2%. This example radar framing structure 312
has been found to yield good performance results. These good
performance results are in terms of good symmetric Doppler
interference mitigation, gesture recognition, and presence
detection while also yielding good power efficiency results in the
application context of a handheld smartphone in a low-power state.
Generation of the radar transmit signal 306 (of FIG. 3-1) and the
processing of the radar receive signal 308 (of FIG. 3-1) are
further described with respect to FIG. 4.
FIG. 4 illustrates an example antenna array 212 and an example
transceiver 214 of the radar system 102. In the depicted
configuration, the transceiver 214 includes a transmitter 402 and a
receiver 404. The transmitter 402 includes at least one
voltage-controlled oscillator 406 and at least one power amplifier
408. The receiver 404 includes at least two receive channels 410-1
to 410-M, where M is a positive integer greater than one. Each
receive channel 410-1 to 410-M includes at least one low-noise
amplifier 412, at least one mixer 414, at least one filter 416, and
at least one analog-to-digital converter 418.
The antenna array 212 includes at least one transmit antenna
element 420 and at least two receive antenna elements 422-1 to
422-M. The transmit antenna element 420 is coupled to the
transmitter 402. The receive antenna elements 422-1 to 422-M are
respectively coupled to the receive channels 410-1 to 410-M.
Although the radar system 102 of FIG. 4 is shown to include
multiple receive antenna elements 422-1 to 422-M and multiple
receive channels 410-1 to 410-M, the described techniques for
symmetric Doppler interference mitigation can also be applied to
radar systems 102 that utilize a single receive antenna element 422
and a single receive channel 410.
During transmission, the voltage-controlled oscillator 406
generates a frequency-modulated radar signal 424 at radio
frequencies. The power amplifier 408 amplifies the
frequency-modulated radar signal 424 for transmission via the
transmit antenna element 420. The transmitted frequency-modulated
radar signal 424 is represented by the radar transmit signal 306,
which can include multiple chirps 310-1 to 310-N based on the radar
framing structure 312 of FIG. 3-2. As an example, the radar
transmit signal 306 is generated according to the burst-mode
feature frame 320 of FIG. 3-2 and includes 16 chirps 310 (e.g., N
equals 16).
During reception, each receive antenna element 422-1 to 422-M
receives a version of the radar receive signal 308-1 to 308-M. In
general, relative phase differences between these versions of the
radar receive signals 308-1 to 308-M are due to differences in
locations of the receive antenna elements 422-1 to 422-M. Within
each receive channel 410-1 to 410-M, the low-noise amplifier 412
amplifies the radar receive signal 308, and the mixer 414 mixes the
amplified radar receive signal 308 with the frequency-modulated
radar signal 424. In particular, the mixer performs a beating
operation, which downconverts and demodulates the radar receive
signal 308 to generate a beat signal 426.
A frequency of the beat signal 426 represents a frequency
difference between the frequency-modulated radar signal 424 and the
radar receive signal 308, which is proportional to the slant range
304 of FIG. 3-1. Although not shown, the beat signal 426 can
include multiple frequencies, which represents reflections from
different portions of the user 302 (e.g., different fingers,
different portions of a hand, or different body parts). In some
cases, these different portions move at different speeds, move in
different directions, or are positioned at different slant ranges
relative to the radar system 102.
The filter 416 filters the beat signal 426, and the
analog-to-digital converter 418 digitizes the filtered beat signal
426. The receive channels 410-1 to 410-M respectively generate
digital beat signals 428-1 to 428-M, which are provided to the
system processor 216 for processing. The receive channels 410-1 to
410-M of the transceiver 214 are coupled to the system processor
216, as shown in FIG. 5.
FIG. 5 illustrates an example scheme implemented by the radar
system 102 for performing symmetric Doppler interference
mitigation. In the depicted configuration, the system processor 216
implements the hardware-abstraction module 220 and the interference
mitigation module 222. The system processor 216 is connected to the
receive channels 410-1 to 410-M. The system processor 216 can also
communicate with the computer processor 202. Although not shown,
the hardware-abstraction module 220 and/or the interference
mitigation module 222 can be implemented by the computer processor
202.
In this example, the hardware-abstraction module 220 accepts the
digital beat signals 428-1 to 428-M from the receive channels 410-1
to 410-M. The digital beat signals 428-1 to 428-M represent raw or
unprocessed complex radar data. The hardware-abstraction module 220
performs one or more operations to generate hardware-agnostic radar
data 502-1 to 502-M based on digital beat signals 428-1 to 428-M.
The hardware-abstraction module 220 transforms the complex radar
data provided by the digital beat signals 428-1 to 428-M into a
form that is expected by the interference mitigation module 222. In
some cases, the hardware-abstraction module 220 normalizes
amplitudes associated with different transmit power levels or
transforms the complex radar data into a frequency-domain
representation.
The hardware-agnostic radar data 502-1 to 502-M can include
magnitude information or both magnitude and phase information
(e.g., in-phase and quadrature components). In some
implementations, the hardware-agnostic radar data 502-1 to 502-M
includes range-Doppler maps for each receive channel 410-1 to 410-M
and for a particular active feature frame 316, as further described
with respect to FIGS. 6 and 7.
The interference mitigation module 222 generates filtered radar
data 504 based on the hardware-agnostic radar data 502-1 to 502-M.
As an example, the filtered radar data 504 includes filtered
range-Doppler maps with interference artifacts that have been
attenuated. The filtered radar data 504 can be provided to other
modules within the radar system 102, such as a gesture-recognition
module, a presence-detection module, a collision-avoidance module,
a vital-sign measurement module, and so forth. These modules
produce radar-application data 506, which is provided to the
radar-based application 206 of FIG. 2-1. Operation of the
hardware-abstraction module 220 is further described with respect
to FIG. 6.
FIG. 6 illustrates an example hardware-abstraction module 220 for
performing symmetric Doppler interference mitigation. In the
depicted configuration, the hardware-abstraction module 220
includes a pre-processing stage 602 and a signal-transformation
stage 604. The pre-processing stage 602 operates on each chirp
310-1 to 310-N within the digital beat signals 428-1 to 428-M. In
other words, the pre-processing stage 602 performs an operation for
each active radar frame 322. In this example, the pre-processing
stage 602 includes M one-dimensional (1D) Fast-Fourier Transform
(FFT) modules, which respectively process the digital beat signals
428-1 to 428-M. Other types of modules that perform similar
operations are also possible, such as a Fourier Transform
module.
For simplicity, the hardware-abstraction module 220 is shown to
process a digital beat signal 428-1 associated with the receive
channel 410-1. The digital beat signal 428-1 includes the chirps
310-1 to 310-M, which are time-domain signals. The chirps 310-1 to
310-M are passed to a one-dimensional FFT module 606-1 in an order
in which they are received and processed by the transceiver 214.
Assuming the radar receive signals 308-1 to 308-M include 16 chirps
310-1 to 310-N (e.g., N equals 16), the one-dimensional FFT module
606-1 performs 16 FFT operations to generate pre-processed complex
radar data per chirp 612-1.
The signal-transformation stage 604 operates on the sequence of
chirps 310-1 to 310-M within each of the digital beat signals 428-1
to 428-M. In other words, the signal-transformation stage 604
performs an operation for each active feature frame 316. In this
example, the signal-transformation stage 604 includes M buffers and
M two-dimensional (2D) FFT modules. For simplicity, the
signal-transformation stage 604 is shown to include a buffer 608-1
and a two-dimensional FFT module 610-1.
The buffer 608-1 stores a first portion of the pre-processed
complex radar data 612-1, which is associated with the first chirp
310-1. The one-dimensional FFT module 606-1 continues to process
subsequent chirps 310-2 to 310-N, and the buffer 608-1 continues to
store the corresponding portions of the pre-processed complex radar
data 612-1. This process continues until the buffer 608-1 stores a
last portion of the pre-processed complex radar data 612-1, which
is associated with the chirp 310-M.
At this point, the buffer 608-1 stores pre-processed complex radar
data associated with a particular feature frame 614-1. The
pre-processed complex radar data per feature frame 614-1 represents
magnitude information (as shown) and phase information (not shown)
across different chirps 310-1 to 310-N and across different range
bins 616-1 to 616-A, where A represents a positive integer.
The two-dimensional FFT 610-1 accepts the pre-processed complex
radar data per feature frame 614-1 and performs a two-dimensional
FFT operation to form the hardware-agnostic radar data 502-1, which
represents a range-Doppler map 620. The range-Doppler map 620
includes complex radar data for the range bins 616-1 to 616-A and
Doppler bins 618-1 to 618-B, where B represents a positive integer.
In other words, each range bin 616-1 to 616-A and Doppler bin 618-1
to 618-B includes a complex number with real and imaginary parts
that together represent magnitude and phase information. The
quantity of range bins 616-1 to 616-A can be on the order of tens
or hundreds, such as 64 or 128 (e.g., A equals 64 or 128). The
quantity of Doppler bins can be on the order of tens or hundreds,
such as 32, 64, or 124 (e.g., B equals 32, 64, or 124). As
described above with respect to FIGS. 1 and 3-1, the range-Doppler
map 620 can include an interference artifact, as further described
with respect to FIG. 7.
FIG. 7 illustrates an example range-Doppler map 620 for performing
symmetric Doppler interference mitigation. In this example, the
amplitude (or magnitude) information of the hardware-agnostic radar
data 502 is illustrated with different patterns. Larger amplitudes
are represented with patterns that have a larger percentage of
black. Smaller amplitudes are represented with patterns that have a
smaller percentage of black (e.g., a higher percentage of white).
Although not shown, the range-Doppler map 620 can also include
phase information.
Each range bin 616 and Doppler bin 618 contains amplitude
information for a particular range interval and Doppler frequency
interval. The range bins 616 are labeled from 1 to A. The Doppler
bins 618 are labeled from -B/2 to 0 to B/2. The zero Doppler bin
618 includes amplitude information for objects that have a Doppler
frequency of 0 Hz or a Doppler frequency equal to a multiple of the
pulse repetition frequency (PRF). The .+-.B/2 bins include
amplitude information for objects that have a Doppler frequency of
.+-.PRF/2.
In this example, the radar receive signal 308 includes reflections
from a hand 702 of the user 302 (of FIG. 3) and reflections from a
body 704 of the user 302. The hand 702 and the body 704 have a
medium-low amplitudes at different range bins 616. In this case,
the body 704 is relatively stationary and appears within the zero
and negative one Doppler bins 618. The hand 702 appears within the
negative two and negative one Doppler bins 618. In most situations,
the desired object (or user 302) contributes to amplitudes within a
few Doppler bins 618 that are either on the positive side or the
negative side of the Doppler spectrum. As such, a plot of the
amplitude of the object is one-sided and not symmetrical across the
Doppler bins 618 for the range bin 616 corresponding to the slant
range 304 to the object. For example, at 708, the amplitude
response of one of the range bins that includes the hand 702 has a
single peak within the negative Doppler bins 618 and no peak within
the positive Doppler bins 618.
The radar receive signal 308 also includes an interference artifact
706 due to vibration of the radar system 102, vibration of a
component within the smart device 104, or vibration of an object
within the external environment. Due to the back and forth motion
of the vibration, the interference artifact 706 contributes to
amplitudes of both positive and negative Doppler bins, such as the
negative two and positive two Doppler bins 618. An amplitude of the
interference artifact 706 is also approximately symmetric for one
or more range bins 616. An example amplitude plot of the
interference artifact 706 for the first range bin 616 is shown at
710. Note that an amplitude of the interference artifact 706 is
greater than an amplitude of the hand 702 in this example.
As shown at 710, the amplitude of the interference artifact 706 is
approximately symmetric across the Doppler bins 618. In other
words, a peak at one of the positive Doppler bins 618 corresponds,
or essentially corresponds, to another peak at one of the negative
Doppler bins 618. In this example, a peak occurs at the positive
two Doppler bin 618 and a corresponding peak, or essentially
corresponding peak, occurs at the negative one Doppler bin 618. As
described, the corresponding positive and negative Doppler bins 618
do not have to be exactly the same (e.g., the highest part of the
peaks do not have to occur within the positive two and negative two
Doppler bins 618 or the positive one and negative one Doppler bins
618). Instead, the corresponding positive and negative Doppler bins
618 can be within some window depending on the resolution of the
Doppler bins 618 (e.g., within two Doppler bins 618 of the opposite
Doppler bin 618, within three Doppler bins 618 of the opposite
Doppler bin 618, and so forth). This interval can include a
quantity of Doppler bins 618 that represent a fraction of the
pulse-repetition frequency, such as less than ten percent or less
than twenty percent, for example. In some cases, the amplitudes of
these peaks are approximately equal to each other (e.g., within ten
to twenty percent of each other or less).
In another example not shown, the amplitude of the interference
artifact 706 is symmetric across the Doppler bins 618. In other
words, a peak occurs at one of the positive Doppler bins 618 (e.g.,
the positive one Doppler bin 618) and another peak occurs at a
corresponding negative Doppler bin 618 (e.g., the negative one
Doppler bin 618).
In other examples not shown, the interference artifact 706 can
contribute to the amplitudes of all of the Doppler bins 618.
Sometimes, some frequency components of the interference artifact
706 that are greater than half of the pulse repetition frequency
experience aliasing. As an example, the pulse repetition frequency
of the radar system 102 can be approximately two kilohertz. In this
case, a portion of the interference artifact 706 can wrap around
the Doppler spectrum and encompass both the .+-.B/2 Doppler bins
618 and .+-.1 Doppler bins 618. In some cases, the interference
artifact 706 is observed across multiple range bins 616. The
quantity of range bins 616 depends on the range bin resolution and
interactions between the radar signals and an interior of the smart
device 104. As an example, the interference artifact 706 can space
across multiple range bins 616 that represent a range that is less
than or equal to 25 centimeters (cm).
The interference mitigation module 222 exploits the symmetric
amplitude of the interference artifact 706 across the Doppler bins
618 to attenuate the interference artifact 706 without
significantly attenuating desired objects, such as the hand 702 or
the body 704, as further described with respect to FIG. 8-1.
FIG. 8-1 illustrates an example implementation of a interference
mitigation module 222 for symmetric Doppler interference
mitigation. In the example, the interference mitigation module 222
includes a noise floor estimation module 802, a comparison module
804, and a noise-floor scaling module 806. The interference
mitigation module 222 can optionally include a bypass module 808
and a residual noise filter module 810 to further improve symmetric
Doppler interference mitigation.
During operation, the interference mitigation module 222 receives
at least one range-Doppler map 620, such as the range-Doppler map
620 of FIG. 7. Although not shown, the interference mitigation
module 222 can sequentially or concurrently process multiple
range-Doppler maps 620, such as those that correspond to the
different receive channels 410-1 to 410-M. Similar operations that
are described with respect to the range-Doppler map 620 are applied
to the remaining range-Doppler maps 620.
During operation, the noise floor estimation module 802 analyzes
the range-Doppler map 620 to produce a noise-floor estimate 812. In
some cases, the noise floor estimation module 802 determines the
noise-floor estimate 812 based on a particular set of range bins
616 and Doppler bins 618. These range bins 616 and Doppler bins 618
can exclude those that are likely to be affected by the
interference artifact 706 or other stationary objects.
Consider FIG. 8-2, which illustrates example regions within the
range-Doppler map 620 (of FIG. 7) for estimating a noise level. In
particular, a first noise-estimation window 814-1 and a second
noise-estimation window 814-2 identify range bins 616 and Doppler
bins 618 for generating the noise-floor estimate 812. In this case,
the noise-estimation windows 814-1 and 814-2 do not include the
Doppler bins 618 associated with stationary objects or objects with
range rates that appear in the low Doppler bins 618 (e.g., the 0
and .+-.1 Doppler bins 618). Additionally, the noise-estimation
windows 814-1 to 814-2 avoid a first few range bins 616 in which
the interference artifact 706 may be present. As an example, the
noise-estimation windows 814-1 to 814-2 do not include range bins
616 that represent slant ranges 304 that are less than 25 cm.
In some cases, one or more of the noise-estimation windows 814-1 or
814-2 include a bin associated with one or more desired objects.
However, due to the large number of bins that are not associated
with a desired object, inclusion of a desired object, such as the
hand 702 within the noise-estimation window 814-1, does not
significantly impact the noise-floor estimate 812.
The noise floor estimation module 802 computes an average amplitude
of the bins within the noise-estimation windows 814-1 and 814-2 to
determine the noise-floor estimate 812. In other cases, the noise
floor estimation module 802 computes a noise-floor estimate 812 for
each bin by computing a local average (e.g., averaging the
amplitude of each bin with its neighboring bins).
Returning to FIG. 8-1, the bypass module 808 analyzes the
range-Doppler map 620 to determine whether or not a desired object
contributes to a peak at the zero Doppler bin 618 or the
neighboring.+-.1Doppler bins 618. If a desired object is detected,
the bypass module 808 provides a bypass indicator 816 to the
comparison module 804, which directs the comparison module 804 to
not filter the low Doppler bins 618, such as the .+-.1 Doppler bins
618. Alternatively, if the bypass module 808 determines that there
is not a desired object within the low Doppler bins 618, the bypass
indicator 816 directs the comparison module 804 to filter the low
Doppler bins 618.
The bypass module 808 makes this determination by analyzing a shape
of a peak within the zero and .+-.1 Doppler bins 618. If the bypass
module 808 detects a single peak within these bins, the bypass
module 808 determines that a desired object is present.
Alternatively, if the bypass module 808 detects two peaks across
any of these bins, the bypass module 808 determines that a desired
object is not present. If a desired object is not present, the
comparison module 804 applies a filter that attenuates the detected
peaks. Otherwise, if a desired object is present, the comparison
module 804 does not apply the filter.
The comparison module 804 compares amplitudes of the positive
Doppler bins 618 to amplitudes of the corresponding negative
Doppler bins 618 for each range bin 616. In one example, the
comparison module 804 scales an amplitude of a first positive
Doppler bin 618 (e.g., the positive one Doppler bin) by an
amplitude of the corresponding first negative Doppler bin 618
(e.g., the negative one Doppler bin). This process continues for
other Doppler bins 618 such that the amplitudes of the positive
two, three . . . B/2 Doppler bins 618 are scaled by amplitudes of
the corresponding negative two, negative three . . . -B/2 Doppler
bins 618.
Amplitudes of the negative Doppler bins 618 are similarly adjusted.
For example, the first negative Doppler bin 618 (e.g., negative one
Doppler bin) is scaled by the original amplitude of the first
positive Doppler bin 618 (e.g., the positive one Doppler bin). Note
that if the bypass indicator 816 indicates that a desired object is
present within the low Doppler bins 618 (e.g., the zero Doppler
bin, the positive one Doppler bin, and the negative one Doppler
bin), the comparison module 804 does not adjust the amplitude of
these bins 618.
This filtering operation is further characterized by Equations 1
and 2, which computes the scaled amplitudes of a positive Doppler
bin or a negative Doppler bin:
.function..function..function..times..times..function..function..function-
..times..times. ##EQU00001## where A.sub.p [x] represents the
scaled amplitude of a positive "x" Doppler bin, A.sub.n[x]
represents the scaled amplitude of a negative "x" Doppler bin,
A.sub.p[x] represents the original amplitude of the positive "x"
Doppler bin, and A.sub.n[x] represents the original amplitude of
the negative "x" Doppler bin.
Other operations can alternatively be performed by the comparison
module 804. For example, the comparison module 804 can perform a
subtraction operation to determine the difference in amplitudes
between the corresponding Doppler bins 618. In this case, the
comparison module 804 decreases an amplitude of the positive one
Doppler bin 618 by the amplitude of the negative one Doppler bin
618, and similarly decreases the amplitude of the negative one
Doppler bin 618 by the original amplitude of the positive one
Doppler bin 618.
In general, the operation performed by the comparison module 804
exploits the symmetric property of the interference artifact 706 to
attenuate the interference artifact 706 and produce the scaled
range-Doppler map 818. Because the desired object (e.g., the hand
702 or the body 704) is not symmetric across the Doppler spectrum,
the amplitude of the desired object is scaled by a value that is
representative of the noise floor. Because this value is
significantly smaller than the peak amplitude of the interference
artifact, the scaled amplitude of the interference artifact 706 can
become smaller than the scaled amplitude of the desired object
within the scaled range-Doppler map 818.
To reduce the scaling of the desired object, the noise-floor
scaling module 806 multiplies the scaled range-Doppler map 818 by
the noise-floor estimate 812. This causes the Doppler bins 618
associated with the interference artifact 706 to have amplitudes
that are approximately equal to the noise floor. The amplitudes
associated with the body 704 or the hand 702, however, remain
relatively unchanged as the noise floor estimate 812 is
approximately equal to the value by which the comparison module 804
scaled the desired object. The resulting output of the noise-floor
scaling module 806 is a filtered range-Doppler map 820.
In some implementations, the residual noise filter module 810 can
further process the filtered range-Doppler map 820 to remove noise
that results due to the operations performed by the comparison
module 804 and the noise-floor scaling module 806. This can include
providing a filter that smooths the amplitudes across the range
bins 616 and/or Doppler bins 618. The residual noise filter module
810 can be implemented as a low-pass filter, a median filter, a
filter that operates across one dimension (e.g., operates on the
range bins 616 or the Doppler bins 618), a filter that operates on
two dimensions (e.g., operates on both the range bins 616 and the
Doppler bins 618), or some combination thereof.
The interference mitigation module 222 is also not limited to only
analyzing and adjusting the amplitude of the range-Doppler map 620.
In some implementations, the interference mitigation module 222
additionally operates on the phase information within the
range-Doppler map 620. Consider an example in which the
interference artifact 706 causes the phases of the positive Doppler
bins and phases of the negative Doppler bins to be in-phase or out
of phase. In this case, the interference mitigation module 222 can
recognize this characteristic to determine whether or not the
interference artifact 706 is present. If the interference artifact
706 is present, the interference mitigation module 222 activates
the comparison module 804 to filter the interference artifact 706.
Otherwise, the filtering operation is bypassed so that the system
processor 216 operates on the range-Doppler map 620 instead of the
filtered range-Doppler map 820. In some cases, the interference
mitigation module 222 can analyze the phase information to
determine an amount to suppress the interference artifact 706.
In some cases, the interference mitigation module 222 operates on a
portion of the range bins 616. If the interference artifact 706 is
likely to appear within a particular set of range bins 616, for
instance, the interference mitigation module 222 can perform the
actions described above for this set of range bins 616 and not
process the remaining range bins 616. As an example, the set of
range bins 616 can include the first five range bins 616, the first
seven range bins 616, or the first ten range bins 616. This can
increase efficiency of the interference mitigation module 222 and
enable the interference mitigation module 222 to operate on
range-Doppler maps 620 that have a large quantity of range bins 616
and/or Doppler bins 618.
Example Method
FIG. 9 depicts an example method 900 for performing operations of a
smart-device-based radar system capable of symmetric Doppler
interference mitigation. Method 900 is shown as sets of operations
(or acts) performed but not necessarily limited to the order or
combinations in which the operations are shown herein. Further, any
of one or more of the operations may be repeated, combined,
reorganized, or linked to provide a wide array of additional and/or
alternate methods. In portions of the following discussion,
reference may be made to the environment 100-1 to 100-4 of FIG. 1,
and entities detailed in FIG. 2-1 or 8-1, reference to which is
made for example only. The techniques are not limited to
performance by one entity or multiple entities operating on one
device.
At 902, a radar transmit signal is transmitted. For example, the
radar system 102 uses at least one transmit antenna element 420 to
transmit the radar transmit signal 306, as shown in FIG. 4. In some
implementations, the radar transmit signal 306 includes multiple
chirps 310-1 to 310-N, whose frequencies are modulated, as shown in
FIG. 3.
At 904, a radar receive signal is received. The radar receive
signal includes an interference artifact and a version of the radar
transmit signal that is reflected by at least one object. For
example, the radar system 102 uses at least one receive antenna
element 422 to receive a version of the radar receive signal 308
that is reflected by the user 302, as shown in FIGS. 3-1 and 4. The
radar receive signal 308 can also include the interference artifact
706 shown in FIG. 7. The interference artifact 706 can occur due to
vibration of the radar system 102 or vibration of other objects
detected by the radar system 102.
At 906, a range-Doppler map is generated based on the radar receive
signal. The interference artifact contributes to amplitudes of both
positive and negative Doppler bins of the range-Doppler map for at
least one range bin. For example, the hardware-abstraction module
220 generates the range-Doppler map 620, as shown in FIG. 6. Across
at least one range bin 616 within the range-Doppler map 620 (e.g.,
such as the first range bin 616), the interference artifact 706
contributes to amplitudes of both positive and negative Doppler
bins 618, such as the .+-.1, .+-.2, and .+-.3 Doppler bins 618. In
particular, the interference artifact 706 has an approximately
symmetric amplitude across the Doppler bins 618, as shown at
710.
At 908 the interference artifact within the range-Doppler map is
filtered to attenuate the interference artifact and generate a
filtered range-Doppler map. For example, the interference
mitigation module 222 filters the range-Doppler map 620 to
attenuate the interference artifact 706 and generate the filtered
range-Doppler map 818, as shown in FIG. 8-1.
At 910, the filtered range-Doppler map is analyzed to detect the at
least one object. For example, the system processor 216 analyzes
the filtered range-Doppler map 818 to detect the at least one
object. The system processor 216 can further determine one or more
characteristics about the object, such as the object's relative
position (e.g., range, azimuth and/or elevation), movement, or
composition. The system processor 216 can also recognize a gesture
performed by a user, measure a vital-sign of the user, provide
collision avoidance, and so forth.
Example Computing System
FIG. 10 illustrates various components of an example computing
system 1000 that can be implemented as any type of client, server,
and/or computing device as described with reference to the previous
FIG. 2-1 to implement symmetric Doppler interference
mitigation.
The computing system 1000 includes communication devices 1002 that
enable wired and/or wireless communication of device data 1004
(e.g., received data, data that is being received, data scheduled
for broadcast, or data packets of the data). Although not shown,
the communication devices 1002 or the computing system 1000 can
include one or more radar systems 102. The device data 1004 or
other device content can include configuration settings of the
device, media content stored on the device, and/or information
associated with a user 302 of the device. Media content stored on
the computing system 1000 can include any type of audio, video,
and/or image data. The computing system 1000 includes one or more
data inputs 1006 via which any type of data, media content, and/or
inputs can be received, such as human utterances, the radar-based
application 206, user-selectable inputs (explicit or implicit),
messages, music, television media content, recorded video content,
and any other type of audio, video, and/or image data received from
any content and/or data source.
The computing system 1000 also includes communication interfaces
1008, which can be implemented as any one or more of a serial
and/or parallel interface, a wireless interface, any type of
network interface, a modem, and as any other type of communication
interface. The communication interfaces 1008 provide a connection
and/or communication links between the computing system 1000 and a
communication network by which other electronic, computing, and
communication devices communicate data with the computing system
1000.
The computing system 1000 includes one or more processors 1010
(e.g., any of microprocessors, controllers, and the like), which
process various computer-executable instructions to control the
operation of the computing system 1000 and to enable techniques
for, or in which can be embodied, gesture recognition in the
presence of saturation. Alternatively or in addition, the computing
system 1000 can be implemented with any one or combination of
hardware, firmware, or fixed logic circuitry that is implemented in
connection with processing and control circuits which are generally
identified at 1012. Although not shown, the computing system 1000
can include a system bus or data transfer system that couples the
various components within the device. A system bus can include any
one or combination of different bus structures, such as a memory
bus or memory controller, a peripheral bus, a universal serial bus,
and/or a processor or local bus that utilizes any of a variety of
bus architectures.
The computing system 1000 also includes a computer-readable media
1014, such as one or more memory devices that enable persistent
and/or non-transitory data storage (i.e., in contrast to mere
signal transmission), examples of which include random access
memory (RAM), non-volatile memory (e.g., any one or more of a
read-only memory (ROM), flash memory, EPROM, EEPROM, etc.), and a
disk storage device. The disk storage device may be implemented as
any type of magnetic or optical storage device, such as a hard disk
drive, a recordable and/or rewriteable compact disc (CD), any type
of a digital versatile disc (DVD), and the like. The computing
system 1000 can also include a mass storage media device (storage
media) 1016.
The computer-readable media 1014 provides data storage mechanisms
to store the device data 1004, as well as various device
applications 1018 and any other types of information and/or data
related to operational aspects of the computing system 1000. For
example, an operating system 1020 can be maintained as a computer
application with the computer-readable media 1014 and executed on
the processors 1010. The device applications 1018 may include a
device manager, such as any form of a control application, software
application, signal-processing and control module, code that is
native to a particular device, a hardware abstraction layer for a
particular device, and so on.
The device applications 1018 also include any system components,
engines, or managers to implement symmetric Doppler interference
mitigation. In this example, the device applications 1018 includes
the radar-based application 206 and the interference mitigation
module 224 of FIG. 2-1.
CONCLUSION
Although techniques using, and apparatuses including, a
smart-device-based radar system performing symmetric Doppler
interference mitigation have been described in language specific to
features and/or methods, it is to be understood that the subject of
the appended claims is not necessarily limited to the specific
features or methods described. Rather, the specific features and
methods are disclosed as example implementations of a
smart-device-based radar system performing symmetric Doppler
interference mitigation.
Some examples are described below.
Example 1: A method performed by a radar system, the method
comprising:
transmitting a radar transmit signal using an antenna array of the
radar system;
receiving a radar receive signal using the antenna array, the radar
receive signal including an interference artifact and a version of
the radar transmit signal that is reflected by at least one
object;
generating a range-Doppler map based on the radar receive signal,
the interference artifact contributing to amplitudes of both
positive and negative Doppler bins of the range-Doppler map for at
least one range bin;
filtering the interference artifact within the range-Doppler map to
attenuate the interference artifact and generate a filtered
range-Doppler map; and
analyzing the filtered range-Doppler map to detect the at least one
object.
Example 2: The method of example 1, wherein the amplitudes
associated with the interference artifact are approximately
symmetric across the positive and negative Doppler bins for the at
least one range bin.
Example 3: The method of example 2, wherein:
the amplitude associated with the interference artifact are
approximately symmetric such that a first amplitude peak within a
first positive Doppler bin of the positive Doppler bins corresponds
to a second amplitude peak within a first negative Doppler bin of
the negative Doppler bins;
the first amplitude peak and the second amplitude peak occur within
the at least one range bin;
the first amplitude peak is within twenty percent of the second
amplitude peak; and
the first negative Doppler bin is within at least two Doppler bins
of a negative Doppler bin that corresponds to the first positive
Doppler bin.
Example 4: The method of any preceding example, wherein:
the at least one object contributes to amplitudes of one or more of
the positive Doppler bins or one or more of the negative Doppler
bins for at least one other range bin; and
the filtering of the interference artifact results in the positive
and negative Doppler bins affected by the interference artifact
having a peak amplitude that is smaller than a peak amplitude of
either the one or more positive Doppler bins or the one or more
negative Doppler bins associated with the at least one object for
the at least one other range bin.
Example 5: The method of any preceding example, wherein the
interference artifact represents vibration of the radar system
during at least a portion of time that the radar receive signal is
received.
Example 6: The method of any preceding example, wherein:
the radar system is embedded within a smart device;
the smart device includes a first component; and
the interference artifact represents at least one of the following:
vibration of the at least one first component; or vibration of
another object that is external to the smart device.
Example 7: The method of any preceding example, wherein the
filtering of the interference artifact within the range-Doppler map
comprises:
producing a scaled range-Doppler map by: scaling amplitudes of the
positive Doppler bins by amplitudes of corresponding negative
Doppler bins for each range bin of the range-Doppler map; and
scaling amplitudes of the negative Doppler bins by the amplitudes
of the corresponding positive Doppler bins for each range bin of
the range-Doppler map.
Example 8: The method of example 7, wherein the filtering of the
interference artifact comprises:
estimating a noise floor of the range-Doppler map; and
multiplying the scaled range-Doppler map by the estimated noise
floor to generate the filtered range-Doppler map.
Example 9: The method of example 8, wherein the filtering of the
interference artifact comprises applying a medium filter to the
filtered range-Doppler map, the medium filter comprising at least
one one-dimensional filter or at least one two-dimensional
filter.
Example 10: The method of example 7, wherein:
the filtering of the interference artifact comprises detecting that
at least one other object contributes to amplitudes of low Doppler
bins within the range-Doppler map, the low Doppler bins including
at least a zero Doppler bin and both a positive Doppler bin and a
negative Doppler bin that are next to the zero Doppler bin; and
the scaling the amplitudes of the positive Doppler bins and the
scaling the amplitudes of the negative Doppler bins comprises,
responsive to detecting the at least one other object, scaling the
amplitudes of Doppler bins that do not include the low Doppler
bins.
Example 11: The method of any preceding example, wherein:
the receiving of the radar receive signal comprises receiving
multiple versions of the radar receive signal using different
antenna elements of the radar system;
the generating the range-Doppler map comprises generating multiple
range-Doppler maps that represent the multiple versions of the
radar receive signal; and
the filtering of the interference artifact comprises filtering the
interference artifact within the multiple range-Doppler maps.
Example 12: The method of any preceding example, wherein the at
least one object comprises a user, the method further
comprising:
recognizing a gesture performed by the user by analyzing the
filtered range-Doppler map; or
measuring a vital sign of the user by analyzing the filtered
range-Doppler map.
Example 13: The method of any of examples 1 to 11, wherein the at
least one object comprises a stylus,
the method further comprising recognizing a gesture performed by a
user using the stylus.
Example 14: An apparatus comprising:
a radar system comprising: an antenna array; a transceiver; and a
processor and computer-readable storage media configured to perform
any of the methods of examples 1 to 13.
Example 15: The apparatus of example 14, wherein the apparatus
comprises a smart device, the smart device comprising one of the
following:
a smartphone;
a smart watch;
a smart speaker;
a smart thermostat;
a security camera;
a vehicle; or
a household appliance.
* * * * *